ARLINGTON, Va. - Scores of farmers, politicians, engineers and refiners on Thursday blasted the Obama administration's latest plan for renewable fuels, with Iowa Gov. Terry Branstad accusing the White House of caving to Big Oil and turning its back on rural America.

The Environmental Protection Agency has proposed requiring refiners to use 15.2 billion gallons of renewable fuels in 2014, 3 billion less than the amount written into federal statutes.

Although federal law forces U.S. refiners to incorporate an annually increasing amount of biofuels into the nation's diesel and gasoline supply, the EPA sets each year's specific volume obligations and can waive the statutory guideposts.

During a daylong hearing on the proposal, Branstad said the plan could devastate corn growers in America's heartland. Corn-based ethanol is the main biofuel mixed with U.S. gasoline.

He blamed an oil industry campaign against the 8-year-old renewable fuel standard for fanning fears about gasoline prices and persuading the EPA to lower next year's biofuel targets.

"They've been intimidated on this issue," Branstad said. "The EPA is now caving into the demands of Big Oil."

The Obama administration has made renewable supplies a signature part of its energy policy - even ordering the federal government on Thursday to nearly triple its use of replenishable power sources.

But the EPA's retreat on renewable fuels policy suggests the administration agrees with the oil industry's arguments that refiners are hitting what they call a blend wall - the point where they no longer can mix in enough ethanol to meet the law's volume targets without exceeding a 10 percent limit acceptable for use in all cars and trucks.

Some environmentalists worry about putting more land into agriculture production to supply biofuel factories. Livestock producers say the biofuels requirements are driving up the price of corn they use as feed.

Tension running high

Corn Belt farmers, by contrast, fear that without a robust renewable fuel mandate driving demand, the cost of producing their product will eclipse the price it commands in the market.

And companies hoping to make advanced biofuels made from wood, grass, algae and other materials say the mandate is critical to ensure a market for their still-developing products.

Those tensions were on full display during Thursday's hearing, which stretched late into the evening and included more than 150 witnesses from across the U.S.

Farmers and biofuel manufacturers who implored EPA officials to hike the 2014 requirements sat inches from oil industry lobbyists, who asked the agency to lower the quotas further.

Representatives from Shell, Chevron, Delta Air Lines subsidiary Monroe Energy and oil industry trade groups told the EPA panel that the agency must lower its 2014 proposal to allow room to sell an ethanol-free product coveted by antique car owners and small equipment users.

"EPA failed to recognize that many consumers demand ethanol-free gasoline," said David Whikehart with refiner Marathon Petroleum. "Their use of ethanol-free gasoline is not discretionary, but required for safe operation of engines."

EPA seeking balance

The industry also took issue with the EPA's plan to require 17 million gallons of cellulosic fuel in 2014, with American Petroleum Institute downstream director Bob Greco calling it "aspirational and unreasonable."

When Congress updated the renewable fuel standard in 2007, lawmakers envisioned advanced biofuels made from non-edible material might eventually overtake corn-based ethanol. But the advanced biofuel industry has developed far more slowly than anticipated.

EPA officials said they were attempting to balance two potentially conflicting principles in setting the 2014 numbers - spurring continued growth in the biofuels industry without making it impossible for refiners to comply with mandates.

The EPA is set to make a final decision on the 2014 targets by next spring, but interests on all sides of the debate have threatened legal challenges. Foes of the renewable fuel standards also are pushing Congress to make more fundamental changes to the mandate.